I have an EJ255 turbo in my coupe, with a (supposedly) 16-gallon fuel cell, which physically measures 14+ gallons. On a road trip, I get low 30's (32-33 mpg), low-mid 20's around town. When I first got the car, I would routinely travel with a 1-gallon plastic gas container, secured in the frunk, until I learned how to read the fuel gauge. I never felt comfortable with a portable fuel container, and stopped carrying it within a few weeks.